68000 NV

At this point this is minimal information about 68000 pcb design ..main features:

• • Uses MC68000 running @8Mhz (Can be 10Mhz with 10MHz version of 68000)

  • Comms via DUART MC68681, 2 serial ..  one input and one output parallel port

  • NVram used for both High and Low RAM/ROM ..(2xDS1249 256Kx8Bit chips, or DS1250 512x8 bit chips)

  • GAL22V10 used for all the decoding

  • Being able to at least implement any number of MONITOR type programs to be able to program via assembly/machine language

  • Possible inclusion of higher level programming languages( in addition to the monitor program)

Schematic Diagram

Prototype pcb made ..Top View

When Running with all chips on pcb current consumption about 450mA at 5V.

This is the original prototype where 2 nvRAM chips are used for even/ odd Ram

The pld  file is as follows for the pcb version ..

PLD file

Name            68K ram/rom;

Partno          0001;

Revision        pcbversion_rom_nvRAM_version;

Date            6/8/18;

Designer        mc;

Company         mcoz;

Location        oz;

Assembly        manual;

Device          g22v10;

/** Inputs **/

pin [2..6] = [a19..a23] ;

pin 7 = rnw;

pin 8 = nlds;

pin 9 = nuds;

pin 10 = nas;

pin 11 = sio_ndtack;

/** Outputs **/

pin 23 = !cs_sio;

pin 22 = !cs_ram;

pin 21 = !lwr;

pin 20 = !lrd;

pin 19 = !uwr;

pin 18 = !urd;

pin 17 = !dtack;

pin 16 = rom_nvRAM;

/** Declarations and Intermediate Variable Definitions **/

field ioaddr= [a19..23];

rom_nvRAM_eqn = (ioaddr:[F0XXXX..FFXXXX]);

cs_ram_eqn   = (ioaddr:[00XXXX..7FXXXX] # ioaddr:[F0XXXX..FFXXXX])& !nas ;

cs_sio_eqn   = (ioaddr:[E8XXXX..EFXXXX])&!nas & !nlds ;

/** Logic Equations **/

cs_ram = cs_ram_eqn;

cs_sio = cs_sio_eqn;

dtack =!nas;

lwr = !rnw & !nlds;

lrd = rnw & !nlds;

uwr = !rnw & !nuds;

urd = rnw & !nuds;

rom_nvRAM = rom_nvRAM_eqn;

Image files of 2 memory chips:

• LRHT68K.bin

• URHT68K.bin

Following is a screen capture of the monitor booting up and  display command initiated ..

Note: Try not to use bottom area of the RAM area as it contains the RESET vectors ... if they get overwritten then you need to reprogram the nvRAM chips again with fresh copy of bin files below...

Here is completed PCB using the 68k chip...

 There is few mods to make the PCB operate ...

• • Cut A18 track from 68k chip to nvRAM

  • Connect A18 address from nvRAM chips to pin 16 of GAL chip

  • Connect pins (1) of two nvRAM chips to GND

  • Short out pin 17 to 18 of 68K chip (HLT and RST pins)

  • Connect AS pin to VPA pin of 68K chip (pin 6 to pin 21)

See pics below..

The information about Monitor etc ...see following web pages for more info .. Tiny Giant 68000 SBC